JP5574534B2 - Composite crucible - Google Patents

Description

  The present invention relates to a composite crucible used for manufacturing a silicon crystal and a method for manufacturing the same.

  In recent years, the demand for solar cells has increased further due to consideration of environmental issues and energy issues. Solar cells are roughly classified into two types, “silicon-based solar cells” and “compound semiconductor-based solar cells”, based on the type of semiconductor material used in the power generation unit. Furthermore, silicon-based solar cells are classified into “crystalline silicon-based solar cells” and “amorphous (amorphous) silicon-based solar cells”, and crystalline silicon-based solar cells are classified as “silicon single-crystal solar cells” and “silicon-rich solar cells”. It is classified as “crystalline solar cell”.

  Focusing on the conversion efficiency, which is the most important characteristic as a solar cell, in recent years, compound semiconductor solar cells are the highest of these, reaching nearly 25%, followed by silicon single crystal solar cells at around 20%, Silicon polycrystalline solar cells, amorphous silicon solar cells and the like are about 5 to 15%. On the other hand, when paying attention to the material cost, silicon is the second most element after oxygen on the earth, and it is much cheaper than compound semiconductors. Therefore, silicon solar cells are most widely used. “Conversion efficiency” is a value expressed as a percentage (%) of “the ratio of the energy of light incident on the solar cell that can be converted into electric energy by the solar cell and extracted”. say.

  Next, a method for manufacturing a silicon single crystal solar cell will be briefly described. First, in order to obtain a silicon wafer as a substrate of a solar battery cell, a cylindrical silicon single crystal ingot is manufactured by the Czochralski method (CZ method) or the floating zone melting method (FZ method). For example, in the CZ method, polycrystalline silicon put into a quartz glass crucible is melted by heating, and a silicon single crystal is produced by gradually pulling up while immersing a seed crystal in the obtained silicon melt. Further, the ingot is sliced and processed into a thin wafer having a thickness of, for example, about 300 μm, and the wafer surface (substrate) serving as a solar cell is obtained by removing the processing distortion on the surface by etching the wafer surface with a chemical solution. This wafer is subjected to impurity (dopant) diffusion treatment to form a PN junction surface on one side of the wafer, and then electrodes are formed on both sides, further reducing light energy loss due to light reflection on the sunlight incident side surface. A solar cell is completed by forming an antireflection film for the purpose. In a solar battery, it is important to manufacture a larger area solar cell in order to obtain a larger current. Since the CZ method can easily produce a large-diameter silicon single crystal and is excellent in strength of the produced single crystal, the large-diameter serving as a substrate material for producing a large-area solar cell. It is suitable as a method for obtaining a silicon wafer.

  On the other hand, in the production of silicon polycrystalline solar cells, a casting method in which molten silicon is solidified with a mold (hereinafter also referred to as “casting method”) or a continuous casting method by electromagnetic induction (hereinafter also referred to as “electromagnetic casting method”). Is preferably employed, and the substrate material can be manufactured at a lower cost than the single crystal silicon substrate manufactured by the Czochralski method. In the casting method, high-purity silicon as a raw material is heated and dissolved in a crucible, and a small amount of boron as a dope material is added uniformly, and then solidified in a crucible or poured into a mold and solidified. Since the crucible and mold used in the casting method are required to have excellent heat resistance and shape stability and to have a small impurity content, quartz is used for the crucible and graphite is used for the mold.

  Quartz crucibles used for the production of silicon crystals are required to have a high viscosity at high temperatures that can withstand prolonged pulling or casting. In addition, it is required to be easily manufactured at low cost. Conventional quartz crucibles with high heat resistance strength include those in which the vicinity of the outer surface of the crucible is a layer containing a high concentration of aluminum (Al), the outer surface of which is coated with a crystallization accelerator such as barium (Ba), Those having a stabilization layer formed of alumina, mullite or the like on the outer surface are known (see Patent Documents 1 to 3).

JP 2000-247778 A Special table 2008-507467 JP-T-2004-531449 Japanese Patent Laid-Open No. 1-153579

  However, for example, a conventional quartz glass crucible with an increased aluminum concentration has a relatively high viscosity but does not have sufficient heat resistance for multiple pulling. Further, according to the conventional quartz glass crucible coated with barium on the surface as a crystallization accelerator, the surface of the crucible can be efficiently crystallized and strengthened, but it requires labor of coating and is highly toxic barium. Handling is also a problem. In addition, the conventional quartz glass crucible having a stabilization layer formed on the outer surface is formed by forming a thin layer having a stabilization layer of about 1 mm by a thermal spraying method, and the heat resistance strength of the entire crucible can be increased. It is only reinforced by the layer, and further improvement in strength is required.

  Accordingly, an object of the present invention is to provide a crucible that has a high viscosity at high temperatures and can be used for a long time, and can be manufactured at low cost, and a method for manufacturing the crucible.

  As a result of intensive studies to solve the above problems, the present inventor has found that the durability of the crucible can be improved by providing a mullite reinforcing layer at the upper end of the quartz glass crucible. The quartz glass crucible sometimes falls inward when used for a long time, but when a reinforcing layer is provided at the upper end, such inward fall can be prevented. In addition, the crucible may be entirely or mostly formed of a mullite material, but when a quartz glass layer is formed on the inner surface of the crucible, the crucible is heated due to the difference in thermal expansion coefficient between mullite and quartz glass. There is a risk of cracking inside. However, when only the upper end portion of the rim is used as the reinforcing layer, such a crack does not occur, and it can be used for a long time.

  The present invention has been made based on such technical knowledge, and the composite crucible according to the present invention is provided on the outer surface side of a quartz glass crucible body having a side wall portion and a bottom portion, and an upper end portion of the quartz glass crucible body. The reinforcing layer is made of a mullite material mainly composed of alumina and silica.

  According to the present invention, since the mullite reinforcing layer is provided on the upper end portion of the crucible body made of quartz glass, the heat resistance strength of the upper end portion of the crucible can be increased. Therefore, the strength of the crucible can be maintained, and it can be used for a long time. In addition, since most of the crucible is made of quartz glass, it can be handled in the same manner as conventional quartz glass crucibles and is easy to handle.

  In this invention, it is preferable that the height of the said reinforcement layer is 1/10 or more and 1/2 or less of the height of the said side wall part. When the height of the reinforcing layer is less than 1/10 of the height of the side wall portion, the function as the reinforcing layer is not exhibited and the side wall portion falls down, and the height of the reinforcing layer is This is because when the height of the side wall portion exceeds 1/2, the crucible side wall portion is likely to crack due to the difference in thermal expansion coefficient between the two when the temperature of the crucible is heated.

  In the present invention, it is preferable to further include a buffer layer provided between the reinforcing layer and the quartz glass crucible body and having a concentration gradient in which the aluminum concentration decreases from the upper side to the lower side of the crucible. According to this configuration, it is possible to sufficiently enhance the bondability at the boundary between the mullite reinforcing layer and the quartz glass in the vertical direction.

  In the present invention, the quartz glass crucible body has an opaque quartz glass layer containing a large number of minute bubbles provided on the outer surface side of the crucible and a transparent quartz glass layer provided on the inner surface side of the crucible. preferable. The opaque quartz glass layer can improve the heat retention, heat the silicon melt uniformly, and the transparent quartz glass layer can improve the production yield of silicon single crystals.

  In the present invention, the reinforcing layer may be provided in the same layer as the opaque quartz glass layer with respect to the thickness direction of the crucible, outside the opaque quartz glass layer, It may be provided in contact with the outer surface. In either case, the quartz glass crucible body can be reinforced, and a crucible with little deformation can be provided even when used for a long time.

  In the present invention, it is preferable that the concentration of aluminum contained in the crucible body has a concentration gradient that decreases from the outer surface side to the inner surface side of the crucible body. According to this configuration, since the coefficient of thermal expansion near the inner surface approaches the coefficient of thermal expansion of quartz glass while sufficiently increasing the viscosity on the outer surface side of the crucible body, the bonding force between the two can be increased. Further, impurity contamination of the silicon melt in the crucible can be prevented.

  Further, in order to solve the above-mentioned problem, the method for manufacturing a composite crucible according to the present invention provides a predetermined position in the mold corresponding to the upper end of the crucible while rotating a mold having a cavity matched to the shape of the composite crucible. Filling a mullite raw material powder containing alumina powder and quartz powder at a predetermined ratio, and filling a second quartz powder in a lower region below the upper region filled with the mullite powder; and Filling the third quartz powder inside the layer of mullite raw material powder and the second quartz powder, and heating and melting the mullite raw material powder, the second quartz powder and the third quartz powder. An opaque quartz glass layer provided on the outer surface side of the crucible; a transparent quartz glass layer provided on the inner surface side of the crucible; and a mullite provided on the outer surface side of the upper end of the crucible. It is characterized by comprising a step of forming a strong layer.

  Furthermore, the method for producing a composite crucible according to the present invention comprises a step of forming a quartz glass crucible body having a side wall and a bottom, and a mullite material obtained by sintering a composition mainly composed of alumina and silica. And a step of joining the reinforcing member to the outer peripheral surface side of the upper end portion of the quartz crucible main body.

  As described above, according to the present invention, a composite crucible using a new material that can be used for a long time due to high heat resistance and can be manufactured at low cost, and a method for manufacturing the same are provided. can do.

It is sectional drawing which shows typically the structure of the composite crucible 10 by the 1st Embodiment of this invention. 3 is a graph showing the Al concentration distribution with respect to the thickness direction of a reinforcing layer 14; 4 is a flowchart for schematically explaining an example of a method for manufacturing the composite crucible 10. (A)-(c) is a schematic diagram for demonstrating schematically an example of the manufacturing method of the composite crucible 10. FIG. It is sectional drawing which shows typically the structure of the composite crucible 20 by the 2nd Embodiment of this invention. It is sectional drawing which shows typically the structure of the composite crucible 30 by the 3rd Embodiment of this invention. 4 is a flowchart for schematically explaining an example of a method for manufacturing the composite crucible 30;

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view showing the structure of the composite crucible according to the first embodiment of the present invention.

  As shown in FIG. 1, the composite crucible 10 has a side wall portion 11A and a bottom portion 11B, and has a basic shape as a container for supporting a silicon melt. The side wall portion 11A is a cylindrical portion parallel to the central axis (Z-axis) of the crucible, and the bottom portion 11B of the crucible is a relatively flat portion including an intersection with the central axis of the crucible. Between the bottom part 11B and the side wall part 11A, a curved part 11C, which is a part where the diameter of the side wall part 11A gradually decreases, is provided. The thickness of the crucible varies depending on the part, but is preferably 5 mm or more. This is because the thickness of medium-sized or large crucibles having a diameter of 16 inches (about 400 mm) or more is usually 5 mm or more, and these crucibles are preferably used for long-time production, and the effects of the present invention are remarkable.

A feature of the composite crucible 10 according to the present embodiment is that a quartz glass crucible is used as a basic structure, and mullite (3Al ₂ O ₃ .2SiO ₂ ) is used as a reinforcing member. Therefore, the composite crucible 10 includes a quartz glass crucible body 11 for supporting the silicon melt, and a mullite reinforcing layer 14 provided at the upper end of the quartz glass crucible body 11. In addition, “composite crucible” means only a crucible composed of mullite and quartz glass instead of using only conventional quartz glass, and the name Therefore, the present invention should not be construed as being limited.

  The quartz glass crucible body 11 includes an opaque quartz glass layer 12 provided on the outer surface side of the crucible and a transparent quartz glass layer 13 provided on the inner surface side of the crucible. As shown in the figure, the opaque quartz glass layer 12 and the reinforcing layer 14 constitute a crucible outer layer, and the transparent quartz glass layer 13 constitutes a crucible inner layer covering the inner surfaces of the opaque quartz glass layer 12 and the reinforcing layer 14. Yes.

  The opaque quartz glass layer 12 is an amorphous silica glass layer containing a large number of minute bubbles. In the present specification, “opaque” means a state in which a large number of bubbles are inherently present in quartz glass and apparently cloudy. The opaque quartz glass layer 12 plays a role of uniformly transferring heat from the heater disposed on the outer periphery of the crucible to the silicon melt in the quartz glass crucible. Since the opaque quartz glass layer 12 has a larger heat capacity than the transparent quartz glass layer 13, the temperature of the silicon melt can be easily controlled.

The bubble content of the opaque quartz glass layer 12 is higher than that of the transparent quartz glass layer 13 and is not particularly limited as long as its function can be exhibited, but it is preferably 0.7% or more. This is because the function of the opaque quartz glass layer 12 cannot be exhibited when the bubble content of the opaque quartz glass layer 12 is less than 0.7%. The bubble content of the opaque quartz glass layer 12 can be determined from the specific gravity. When an opaque quartz glass piece of unit volume (1 cm ³ ) is cut out from the crucible and its mass is A, if the specific gravity B of quartz glass not containing bubbles is 2.21 g / cm ³ , the bubble content is P (%) = (A / B) × 100.

  The transparent quartz glass layer 13 is an amorphous silica glass layer substantially free of bubbles. According to the transparent quartz glass layer 13, it is possible to prevent an increase in the number of quartz pieces peeled from the inner surface of the crucible, and to increase the silicon single crystallization rate. Here, “substantially free of bubbles” means that the bubble content and bubble size are such that the single crystallization rate does not decrease due to bubbles, and is not particularly limited, It is preferable that the bubble content is 0.1% or less and the average diameter of the bubbles is 100 μm or less. The bubble content of the transparent quartz glass layer 13 can be measured nondestructively using an optical detection means. As an optical detection means, an optical camera including a light receiving lens and an imaging unit is used. To measure the bubble content from the surface to a certain depth, the focus of the light receiving lens is scanned from the surface in the depth direction. Good. The captured image data is subjected to image processing in an image processing apparatus, and the bubble content rate is calculated.

  The change in the bubble content from the opaque quartz glass layer 12 to the transparent quartz glass layer 13 is relatively steep, and 30 μm from the position where the bubble content of the transparent quartz glass layer 13 starts to increase toward the outer surface of the crucible. At a certain degree of progress, the bubble content of the opaque quartz glass layer 12 is reached. Therefore, the boundary between the opaque quartz glass layer 12 and the transparent quartz glass layer 13 is clear and can be easily distinguished visually.

  The transparent quartz glass layer 13 may be natural quartz glass or synthetic quartz glass. Natural quartz glass means silica glass produced using natural silica such as silica and natural quartz as a raw material. In general, natural quartz has the characteristics that the concentration of metal impurities is higher and the concentration of OH groups is lower than that of synthetic quartz. For example, the content of Al contained in natural quartz is 1 ppm or more, the content of alkali metals (Na, K and Li) is 0.05 ppm or more, and the content of OH groups is less than 60 ppm. Since natural quartz has a higher viscosity at high temperatures than synthetic quartz, the heat resistance of the entire crucible can be increased. Natural materials are cheaper than synthetic quartz and are advantageous in terms of cost.

  On the other hand, synthetic quartz glass means silica glass produced using, for example, synthetic silica obtained by hydrolysis of silicon alkoxide as a raw material. In general, synthetic quartz has the characteristics that the concentration of metal impurities is lower than that of natural quartz and the concentration of OH groups is high. For example, the content of each metal impurity contained in synthetic quartz is less than 0.05 ppm, and the content of OH groups is 30 ppm or more. However, since synthetic quartz to which metal impurities such as Al are added is also known, whether or not it is synthetic quartz should not be determined based on one element, but comprehensively based on a plurality of elements. It should be judged. Since synthetic quartz glass has very few impurities compared to natural quartz glass, it is possible to prevent an increase in impurities eluted from the crucible into the silicon melt, and to increase the silicon single crystallization rate.

  The concentration of alkali metals (Na, K and Li) contained in the transparent quartz glass layer 13 is preferably 0.05 ppm or less. This is because when the crucible body 11 contains a large amount of alkali metal, impurities eluted from the crucible into the silicon melt increase, resulting in a deterioration in the quality of the silicon single crystal. The above conditions are required for a crucible used for pulling up a silicon single crystal for a semiconductor device, but in the case of a crucible used for pulling up a silicon crystal for a solar cell, there is no problem even if a relatively large amount of alkali metal is contained. .

  The thickness of the transparent quartz glass layer 13 is preferably 0.5 mm or more. This is because when the transparent quartz glass layer 13 is thinner than 0.5 mm, the transparent quartz glass layer 13 may be completely melted during the pulling of the silicon single crystal, and the crucible body 11 may be exposed. The thickness of the transparent quartz glass layer 13 does not need to be constant from the side wall portion 11A to the bottom portion 11B. For example, the thickness of the transparent quartz glass layer 13 in the curved portion 11C is equal to that of the transparent quartz glass in the side wall portion 11A or the bottom portion 11B. The glass layer 13 may be thicker.

  A reinforcing layer 14 is provided on the outer surface side of the upper end portion of the composite crucible 10. The reinforcing layer 14 is made of a mullite material mainly composed of alumina and silica, and is provided within a range of, for example, 5 to 10 cm below the rim upper end of the crucible.

Mullite is a compound containing silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ) in a predetermined ratio. Mullite is a white opaque material with a melting point of 1850 ° C. Therefore, the heat resistance strength is higher than that of quartz glass. Since mullite has a higher viscosity at high temperatures than quartz glass, the heat resistance of the entire crucible can be increased. In addition, mullite is less expensive than quartz and is very advantageous in terms of cost.

The thermal expansion coefficient of mullite is known to be 4.3 to 4.9 (10 ⁻⁶ K ⁻¹ ), although it varies depending on the ratio between SiO ₂ and Al ₂ O ₃ . On the other hand, the thermal expansion coefficient of Al ₂ O ₃ is 7.8, and the thermal expansion coefficient of quartz glass is 0.56. Although the thermal expansion coefficient of mullite is larger than that of quartz glass, the bonding property between the two is good. If the temperature during heating and cooling is appropriately controlled, the quartz glass crucible body 11 and the reinforcing layer 14 due to the difference in thermal expansion coefficient. And peeling can be prevented. However, considering the difference in thermal expansion coefficient, it is better that the joint surfaces of the two are as small as possible. Therefore, the reinforcing layer 14 is provided only at the upper end of the rim, not the entire crucible.

The height _{H 1} of the reinforcing layer 14, the side wall portion 11A of the crucible with respect to the height _{H 2,} is preferably 0.1H ₂ or more and 0.5H ₂ below. If the height H ₁ of the reinforcing layer 14 is 0.1H ₂ or less with respect to height H ₂ of the side wall portion 11A of the crucible can not effectively function as a reinforcing layer 14, inward fall of the side wall portions This is because there is a risk of occurrence. On the other hand, the crucible is accommodated in, for example, a graphite susceptor in the CZ method, the outer surface of the bottom 11B and the curved portion 11C of the crucible is supported by the graphite susceptor, and the inner surface of the bottom 11B and the curved portion 11C of the crucible is made of silicon melt. Since it is in contact for a long time and receives the weight of the silicon melt, deformation is unlikely to occur. Therefore, the necessity to reinforce the bottom part 11B and the curved part 11C is low. Rather, when more than 0.5H ₂ relative to the height of H ₂ sidewall portion 11A of the crucible, takes thermal stress by both the difference in thermal expansion coefficient during heating of the crucible, possible cracking of the crucible side wall portion occurs High nature. In addition, since aluminum contained in mullite is an impurity for silicon crystals, the use of mullite must be kept to a minimum. For this reason, the height H ₁ of the reinforcing layer 14 is preferably 0.5H ₂ or less.

  FIG. 2 is a graph showing changes in the concentration of Al in the reinforcing layer 14 in the thickness direction.

  As shown in FIG. 2, the concentration of aluminum contained in the mullite reinforcing layer 14 may have a concentration gradient that decreases from the outer surface toward the inner surface. When configured in this way, the coefficient of thermal expansion near the inner surface of the crucible body 11 approaches the coefficient of thermal expansion of quartz glass, so that delamination due to the difference in coefficient of thermal expansion can be prevented, and the bonding force between the two Can be increased. In addition, since the Al concentration on the inner surface side of the crucible is low, the silicon melt in the crucible can be prevented from being contaminated with Al.

  Since the composite crucible 10 according to the present embodiment uses mullite as a reinforcing member of the crucible body 11 made of quartz glass, the composite crucible 10 is superior in durability at a high temperature than the conventional quartz glass crucible. Therefore, it becomes possible to pull up a plurality of silicon single crystals from one crucible by a multi-pulling method in which a silicon raw material is additionally charged, and the manufacturing cost of the silicon single crystal can be greatly reduced. Furthermore, since most of the crucible is made of quartz glass, it can be handled in the same way as conventional quartz glass crucibles, and there is no need to significantly change the temperature control conditions when pulling up the silicon single crystal.

  Since the composite crucible 10 having the mullite reinforcing layer 14 at the upper end of the crucible has a higher impurity concentration (Al concentration) than a crucible made only of quartz glass, a crucible suitable for pulling up a silicon single crystal for semiconductor devices, Is hard to say. However, the inner surface of the crucible in contact with the silicon melt is covered with a transparent quartz glass layer, and the elution of impurities into the silicon melt can be prevented to some extent. Therefore, it is suitable for pulling up a silicon crystal having a high tolerance for impurities such as a silicon crystal for solar cells. Furthermore, since mullite is less expensive than quartz raw material, it is advantageous in terms of cost, and finally, a low-cost silicon wafer can be provided.

  Next, the manufacturing method of the composite crucible 10 is demonstrated in detail, referring FIG.3 and FIG.4.

  FIG. 3 is a flowchart schematically showing the manufacturing process of the composite crucible 10. 4A to 4C are schematic views for explaining a method for manufacturing the composite crucible 10.

  The composite crucible 10 can be manufactured by a rotational mold method. In the rotary molding method, as shown in FIG. 4A, a carbon mold 16 having a cavity matched to the outer shape of the crucible is prepared, and the raw material powder of the crucible is filled while rotating the mold 16, and along the inner surface of the mold. A layer of raw material powder is formed. At this time, the mullite raw material powder 15a is filled in the cavity upper region corresponding to the upper end of the crucible, and the quartz powder (second quartz powder) 15b is filled in the region below the upper end region (step S11). In particular, after filling the quartz powder 15b first, the mullite raw material powder 15a is filled. Since the carbon mold 16 rotates at a constant speed, the filled raw material powder remains at a fixed position while being stuck to the inner surface by centrifugal force, and its shape is maintained.

  The mullite raw material powder 15a is a raw material powder obtained by mixing alumina powder and quartz powder (first quartz powder) at an element ratio of 3: 2. As shown in FIG. 2, in order to vary the Al concentration in the reinforcing layer with respect to the thickness direction of the crucible, prepare a plurality of mullite raw material powders having different ratios of alumina powder and quartz powder, and in order It can be realized by putting it in Further, it is preferable to use natural quartz powder as the quartz powder 15b.

  Next, as shown in FIG. 4 (b), quartz used as a raw material for the transparent quartz glass layer 13 in the mold 16 in which layers of the mullite raw material powder 15a and the quartz powder 15b used as the raw material for the opaque quartz glass layer 12 are formed. The powder 15c (third quartz powder) is filled, and the quartz powder layer is further thickened (step S12). The quartz powder 15c is filled in the entire mold with a predetermined thickness. The quartz powder 15c may be natural quartz powder or synthetic quartz powder.

  Then, as shown in FIG.4 (c), the arc electrode 17 is installed in a cavity, The inside of a mold is heated at the temperature of 1720 degreeC or more, and raw material powder is arc-melted. Further, by simultaneously degassing the quartz powder layer through the ventilation holes provided in the mold simultaneously with this heating, bubbles on the inner surface of the crucible are removed, and a transparent quartz glass layer 13 substantially free of bubbles is formed ( Step S13). Thereafter, the decompression for deaeration is weakened or stopped while continuing the heating, and the bubbles are left, thereby forming the opaque quartz glass layer 12 containing a large number of minute bubbles (step S14). At this time, a large number of minute bubbles remain in the reinforcing layer 14. Then, cut the rim of the crucible and align the height of the top of the crucible. (Step S15). Thus, the composite crucible 10 according to the present embodiment is completed.

  As described above, the method of manufacturing the composite crucible according to the present embodiment forms the mullite reinforcing layer together with the quartz glass layer by arc melting, so that the durability at high temperature is maintained while maintaining the quality of the conventional quartz glass crucible. High-quality crucibles with excellent resistance can be produced efficiently.

  Next, the composite crucible according to the second embodiment of the present invention will be described in detail.

  FIG. 5 is a schematic cross-sectional view showing the structure of the composite crucible according to the second embodiment of the present invention.

  As shown in FIG. 5, the composite crucible 20 according to the present embodiment is characterized in that a buffer layer 18 is provided between the opaque quartz glass layer 12 and the reinforcing layer 14 thereabove. The buffer layer 18 is a layer in which the Al concentration contained in the mullite reinforcing layer 14 gradually decreases from the upper side to the lower side. FIG. 2 shows a case where there is a concentration gradient in the thickness direction of the crucible, but such a concentration gradient is formed in the buffer layer 18 in the vertical direction. According to this configuration, the difference in coefficient of thermal expansion between the opaque quartz glass layer 12 and the mullite reinforcing layer 14 can be absorbed, and cracking due to thermal stress at the joint interface between the two can be prevented.

  FIG. 6 is a schematic cross-sectional view showing the structure of the composite crucible according to the third embodiment of the present invention.

  As shown in FIG. 6, the characteristic of the composite crucible 30 according to the present embodiment is that a mullite reinforcing layer 14 is provided outside the quartz glass crucible body 11. Therefore, the reinforcing layer 14 is in contact with the outer surface of the opaque quartz glass layer 12 constituting the outer layer of the quartz glass crucible body 11. The reinforcing layer 14 is formed by joining and integrating a ring-shaped member prepared separately from the quartz glass crucible body 11 to the outer surface of the quartz glass crucible. Since other configurations are substantially the same as those of the composite crucible 10 according to the first embodiment, the same reference numerals are assigned to the same numbers, and detailed descriptions thereof are omitted.

  FIG. 7 is a flowchart for explaining a method of manufacturing the composite crucible 30.

  As shown in FIG. 7, in the manufacture of the composite crucible 30, first, the quartz glass crucible body 11 is produced (step S21). The quartz glass crucible main body 11 can be produced by the rotational molding method. Unlike the first embodiment, the opaque quartz glass layer 12 is formed up to the upper end of the rim, but the other configurations are substantially the same.

  Next, a mullite ring-shaped reinforcing member to be the reinforcing layer 14 is produced (step S22). The mullite reinforcing member can be produced by, for example, a slip casting method. The slip casting method is well known as a method for forming a ceramic sintered body. Usually, a mold made of a material having water absorption properties such as gypsum is used, and moisture is absorbed from a slurry (ceramic powder suspension or slip) injected into a cavity of the mold to solidify the slurry. Is done. The obtained molded body is degreased and fired to obtain a final product. This method is generally suitable for producing compact shaped bodies, but it takes time to produce a thick shaped body, so slip casting while applying constant pressure to the slurry. There is also known a pressure molding method for performing the above. According to this slip cast pressure molding method, the slurry can be dehydrated forcibly, and a relatively thick molded body can be produced.

  When forming a ring-shaped reinforcing member by slip casting, first, alumina powder and quartz powder, which are raw materials of mullite, are dispersed in water at a predetermined ratio to prepare a slurry, and then a crystallization accelerator is added to the slurry. And further disperse. Further, the slurry is poured into a mold and dehydrated to obtain a molded body of a composition mainly composed of alumina and silica. In the present embodiment, it is preferable to forcibly dehydrate the slurry by attaching the mold to the rotating shaft and rotating the mold. Next, the molded body solidified by dehydration is further dried for a certain period of time, degreased, and then fired at 1400 ° C. to complete a mullite reinforcing member.

  Next, a ring-shaped reinforcing member is fitted to the outside of the rim upper end of the quartz glass crucible main body 11, and both are joined. In this way, the reinforcing layer 14 is formed outside the quartz glass crucible body 11. Thereafter, the quartz glass crucible main body 11 and the reinforcing layer 14 are rim-cut together to align the height of the upper end of the crucible. Although it is possible to align the rim position by adjusting the height when the reinforcing member is fitted into the rim-cut quartz glass crucible body 11, it is difficult to adjust the height. It is preferable to align the height by cutting. Thus, the composite crucible 30 according to the present embodiment is completed.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention, and these are also included in the scope of the present invention. Needless to say.

Example 1
A composite crucible sample A1 was prepared. The size of the crucible was 16 inches in diameter (diameter of about 400 mm), the height was 250 mm, and the wall thickness was 6.5 mm at the straight copper portion, 8 mm at the curved portion, and 5 mm at the bottom. The thickness of the transparent quartz glass layer on the side wall was 0.5 mm, and the thickness of the opaque quartz glass layer on the side wall was 6 mm. Further, a mullite reinforcing layer was provided at the upper end of the crucible. The height H ₂ of the side wall portion was 150 mm, and the height H ₁ of the reinforcing layer was about 15 mm (H ₁ ≈0.1 H ₂ ).

  Next, the crucible sample A1 was continuously heated in the furnace for a long time, and the deformation state of the crucible was confirmed. The heating conditions were as follows. First, the temperature was raised from room temperature to about 1580 ° C. over 5 hours at a substantially constant rate, the temperature of 1580 ° C. was maintained for 25 hours, the temperature was lowered to 1500 ° C., and the temperature of 1500 ° C. was maintained for 100 hours. Then, it cooled at normal speed to normal temperature over 7 hours. This heating test was performed in an empty state in which no silicon raw material was charged in the crucible. In normal use of the crucible, silicon raw material is charged and the wall surface of the crucible is pushed from the inside by the silicon melt, but when there is no silicon melt, there is no such pressing force, Side wall is easy to fall inward. Such a state is similar to the state where the silicon single crystal has been pulled up and the silicon melt in the crucible has been consumed. The results of this heating test are shown in Table 1.

  As shown in Table 1, in the crucible sample A1 having a mullite reinforcing layer having a height of about 15 mm formed on the outer surface side of the upper end portion of the crucible, inclining, buckling, etc. that can be observed with the naked eye in the heating test No deformation occurred. Moreover, there was no crack of the side wall.

(Example 2)
A composite crucible sample A2 having the same structure except that the height H ₁ of the reinforcing layer was about 50 mm (H ₁ = 0.3H ₂ ) was prepared, and the same heating test as in Example 1 was performed. As a result, as shown in Table 1, deformation such as inward tilting and buckling that could be observed with the naked eye did not occur. Moreover, there was no crack of the side wall.

(Example 3)
A composite crucible sample A3 having the same structure except that the height H ₁ of the reinforcing layer was about 75 mm (H ₁ = 0.5H ₂ ) was prepared, and the same heating test as in Example 1 was performed. As a result, as shown in Table 1, deformation such as inward tilting and buckling that could be observed with the naked eye did not occur. Moreover, there was no crack of the side wall.

(Example 4)
Sample of a composite crucible having the same structure except that the height H ₁ of the reinforcing layer is about 100 mm (H ₁ ≈0.7H ₂ ) and a buffer layer of 25 mm is provided between the reinforcing layer and the quartz glass outer layer. A4 was prepared and the same heating test as in Example 1 was performed. As a result, as shown in Table 1, deformation such as inward tilting and buckling that could be observed with the naked eye did not occur.

(Comparative Example 1)
A general quartz glass crucible sample B1 having an inner layer made of a transparent quartz glass layer and an outer layer made of an opaque quartz glass layer was prepared. The crucible had a diameter of 16 inches (diameter of about 400 mm), a height of 250 mm, and a wall thickness of 6.5 mm at the straight copper portion, 8 mm at the curved portion, and 5 mm at the bottom. The thickness of the transparent quartz glass layer on the side wall was 0.5 mm, and the thickness of the opaque quartz glass layer on the side wall was 6 mm. Next, the same heating test as in Example 1 was performed. The results are shown in Table 1.

  As shown in Table 1, in a general quartz glass crucible sample B1, the side wall portion partially fell inward after being heated for a long time, buckling occurred, and the roundness was greatly reduced.

(Comparative Example 2)
A composite crucible sample B2 having the same structure except that the height H ₁ of the reinforcing layer was about 10 mm (H ₁ ≈0.07H ₂ ) was prepared, and the same heating test as in Example 1 was performed. As a result, as shown in Table 1, the side wall portion partially fell inward and buckled.

(Comparative Example 3)
A composite crucible sample B3 having the same structure except that the height H ₁ of the reinforcing layer was about 100 mm (H ₁ ≈0.7H ₂ ) was prepared, and the same heating test as in Example 1 was performed. As a result, as shown in Table 1, many cracks occurred on the inner surface of the side wall.

DESCRIPTION OF SYMBOLS 10 Composite crucible 11 Quartz glass crucible main body 11A Side wall part 11B Bottom part 11C Curved part 12 Opaque quartz glass layer 13 Transparent quartz glass layer 14 Reinforcement layer 15a Mullite raw material powder 15b Quartz powder (second quartz powder)
15c quartz powder (third quartz powder)
16 Carbon mold 17 Arc electrode 18 Buffer layer 20 Composite crucible

Claims (2)

A quartz glass crucible body having a side wall and a bottom;
A reinforcing layer made of a mullite material mainly composed of alumina and silica, provided at the upper end of the quartz glass crucible body ;
A buffer layer provided between the reinforcing layer and the quartz glass crucible body,
The quartz glass crucible body has an opaque quartz glass layer containing a large number of minute bubbles provided on the outer surface side of the crucible, and a transparent quartz glass layer provided on the inner surface side of the crucible,
The reinforcing layer is provided in the same layer as the opaque quartz glass layer with respect to the thickness direction of the crucible, and constitutes the outer surface of the crucible together with the opaque quartz glass layer,
The inner surface of the reinforcing layer is covered with the transparent quartz glass layer,
The composite crucible , wherein the buffer layer has a concentration gradient in which the aluminum concentration decreases from above to below the crucible.   2. The composite crucible according to claim 1, wherein the height of the reinforcing layer is not less than 1/10 and not more than 1/2 of the height of the side wall portion.

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